When the key is turned to the Magneto position after starting on Battery, the engine stops. The problem is that the ignition switch doesn't make contact in the Magneto position. It overruns it. If you stop a little short of the Magneto position, contact is made and the engine continue running. Perhaps the triangular stop is worn too much to stop the switch from stopping in the proper position. How can this be repaired?
I see no one has responded so I will. You did not state what year or what ignition switch brand you are using. I have a 1915 with Ford switch which had the same problem. After pricing new switches, I took the old one out of the car and bent the contacts a little to make better contact. I also cleaned up the contacts and put a little electrical grease on them. Bending is hard to do as there is no way to easily take my apart. I managed enough of a bend so that it now makes good contact.
I have had that problem for years in 2 of my T's on the BAT side. I think it would be an easy fix but live with it for now.
The running gear is 1926 but the ignition switch might be of a different vintage. I think the switch is of the pin type because a local gentleman who really knows Model Ts took it apart by pushing in and turning it pretty much like a bayonet connector.
He found that the small triangle stop wasn't stopping the switch in the proper place to make the connection in Magneto mode. He thought maybe building up one side of the triangle with solder might do the trick, but I don't have the skill to do that job right.
Is there a kit that includes the worn parts that need to be replaced?
Fiddling with the switch could make the connection but that wouldn't be a good way to drive.
If the ignition / light switch and ammeter sits on n oval plate, then it's the '26/'27 style. I've repaired a few of those, but don't know what triangles you refer to?
The switch innards are available fairly cheap if you can't make them work by bending and cleaning. The ignition switching is made by the smaller diameter round part in combination with the back plate: https://www.modeltford.com/item/5012P.aspx
The one I have looks more like the pin type in the Lang's catalog. However, the photo doesn't show the triangle stop. We might have to take it apart again to take a photograph that shows it.
Send it to Ben Martin. He works wonders on these switches. He only works through phone and snail mail. 770-938-3376
Most suppliers are/were out of stock on the parts needed, but you can call and see if they now have them. The contact plate, the part with the pins has detentes in it, you might just have to learn to feel them as you turn the key.